System and method for controlling a vapor dryer process

ABSTRACT

A system and method are disclosed including a vapor dryer chamber ( 12 ) with a lid ( 14 ). A heater ( 16 ) is disposed within the vapor dryer chamber to vaporize liquid drying medium ( 24 ), preferably isopropyl alcohol, in the bottom of the vapor dryer chamber ( 12 ). Cooling coils ( 18 ) disposed within an upper portion of the vapor drying chamber ( 12 ) condense the drying medium vapor. A vapor monitor assembly ( 30 ) is disposed within the vapor dryer chamber ( 12 ) to monitor the vapor concentration within vapor dryer chamber ( 12 ). A controller ( 40 ) is associated with the vapor monitor assembly ( 30 ) and evaluates vapor concentration measurements from the vapor monitor ( 38 ).

This is a divisional application of Ser. No. 09/737,632, now U.S. Pat.No. 6,497,055, filed Dec. 14, 2000, which claims priority under 35 USC119(e)(1) of provisional application Ser. No. 60/174,321, filed Jan. 4,2000.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of electronic devices.More specifically, the invention relates to a system and method forcontrolling vapor dryer processing which is used in the fabrication ofsemiconductor devices.

BACKGROUND OF THE INVENTION

Vapor dryers are often used in semiconductor fabrication processing.Typically, a boat loaded with semiconductor substrate wafers is placedinto a vapor dryer chamber. Heaters along the bottom and/or sides of thevapor dryer chamber heat a drying medium, typically isopropyl alcohol(IPA), to create a vapor cloud of drying medium within the chamber.Cooling coils within an upper portion of the vapor dryer chamber aretypically provided to condense the drying medium vapor. When the vapordryer chamber reaches an equilibrium or steady state, the vapor clouddevelops an upper boundary within the vapor dryer chamber known as avapor blanket.

The boat and semiconductor substrate wafers preferably rest in thechamber beneath the vapor blanket. The drying medium acts to displacewater or other fluid associated with the semiconductor substrate wafers.If water is not displaced from the semiconductor substrate wafers, watercan inhibit the effectiveness of subsequent fabrication processes. Forexample, if not removed, water may etch a silicon wafer. Water may alsocollect and leave behind a deposit when it eventually evaporates. Thedeposit often creates a defect. Water may react with the substratematerial such that deposited material fails to properly adhere to thesubstrate. These types of defects are often referred to as watermarks.

A variety of factors can disrupt the effectiveness of the vapor dryingprocess. Often, before a boat and semiconductor substrate wafers areplaced into the vapor dryer chamber, the chamber has reached anequilibrium or steady state and developed a vapor blanket at a desiredheight within the vapor dryer chamber. When the lid of the vapor dryerchamber is opened, the vapor cloud is disturbed and the vapor blanket nolonger rests at the desired height within the vapor dryer chamber. Thevapor cloud may only partially cover the semiconductor substrate waferssuch that the vapor cloud interacts with only a portion of the wafers.Eventually the vapor dryer chamber may return to its initial equilibriumor steady state with the vapor blanket resting at the desired heightwithin the vapor dryer chamber. However, a portion of the substrates maynot be properly processed because of the disruption of the vaporblanket.

Other factors can effect vapor dryer processing. The number of diskswithin the chamber can effect the time it takes for the chamber toreturn to its equilibrium state. The heater or cooling coils maymalfunction such that the vapor cloud does not develop properly. Anadequate amount of drying medium may not be available to process thesubstrate wafers. Also, an exhaust system associate with the vapor dryerchamber may malfunction, disrupting vapor dryer processing.

Often vapor drying processes are timed. After being processed within thevapor dryer chamber for a desired amount of time, the boat and substratewafers are removed. One problem with using a set time is that the wafersmay not be properly processed if the chamber does not return to itsequilibrium state as quickly as expected. Also, if the heater or coolingcoils are malfunctioning, the substrate wafers may not be processedproperly. Because it often takes days or weeks to discover a watermarkand its source, improper processing can waste valuable time andresources.

Set times are typically conservative, often resulting in the substratewafers remaining within the vapor dryer chamber for a longer period thanis necessary for optimum processing. This practice consumes valuableprocess time within the chamber that could be used to process othersemiconductor substrate wafers.

SUMMARY OF THE INVENTION

In accordance with teachings of the present disclosure, a system andmethod are provided for controlling vapor dryer processing thatsubstantially eliminates or reduce disadvantages and problems associatedwith prior systems and methods for operating a vapor dryer. The vapordryer system preferably includes a vapor dryer chamber with a lid. Aheater may be disposed within the vapor dryer chamber to heat a selectedliquid drying medium, such as IPA, in the bottom of the vapor dryerchamber. Cooling coils may be disposed within an upper portion of thevapor drying chamber condense drying medium vapor. A vapor monitor ispreferably disposed within the vapor dryer chamber to monitor the vaporconcentration at a desired position. A controller is preferablyassociated with the vapor monitor and evaluates vapor concentrationmeasurements from the vapor monitor.

In one aspect of the present invention, a vapor dryer system for use insemiconductor fabrication includes a vapor dryer chamber and at leastone heater disposed within the vapor dryer chamber. The heater creates adrying medium vapor by heating a liquid form of drying medium within thevapor dryer chamber. At least one cooling coil is preferably disposedwithin the vapor dryer chamber to condense the drying medium vapor. Avapor monitor may be disposed within the vapor dryer chamber to measurevapor concentration within the vapor dryer chamber. The vapor monitor ispreferably connected to a controller that evaluates vapor concentrationmeasurements from the vapor monitor. More specifically, the vapormonitor may be an isopropyl alcohol vapor concentration monitor.

In another aspect of the present invention, the drying medium vaporforms a vapor cloud having a desired steady state blanket level withinthe vapor dryer chamber. The vapor monitor is preferably positioned tomeasure the drying medium vapor concentration at the desired steadystate blanket level.

In another aspect of the present invention, a vapor dryer control systemis disclosed for use in semiconductor fabrication. The vapor dryercontrol system includes a vapor monitor to measure vapor concentrationin a vapor dryer chamber and a controller associated with the vapormonitor to evaluate vapor concentration measurements from the vapormonitor. More specifically, the controller may determine a vapor dryerprocess cycle end point. More specifically, the controller may detectand note a vapor dryer process excursion.

In yet another aspect of the present invention a method for monitoring avapor drying process includes providing a vapor monitor in a vapor dryerchamber. The vapor monitor then measures vapor concentration at aselected level of the vapor dryer chamber. The vapor concentrationmeasurements are recorded and used to control the vapor drying process.More specifically, measuring vapor concentration may include measuringthe vapor concentration of isopropyl alcohol within the vapor dryerchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 is a schematic drawing in section with a portion broken away of avapor dryer system incorporating teachings of the present invention; and

FIG. 2 is a flow diagram of a method for controlling a vapor dryerprocess incorporating teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of vapor dryer system 10 incorporatingteachings of the present invention. Vapor dryer system 10 includes vapordrying chamber 12 for processing semiconductor substrate wafers 22. Lid14 is preferably pivotally coupled (not expressly shown) to vapor dryerchamber 12 such that lid 14 allows access to the interior of vapor dryerchamber 12. Heater 16 is disposed within a bottom portion of vapor dryerchamber 12. Cooling coils 18 are disposed within an upper portion ofvapor drying chamber 12. Heater 16 is preferably connected to anexterior power source (not expressly shown) operable to supply power toheater 16. Cooling coils 18 are preferably connected to an exteriorcooling source (not expressly shown) operable to communicate coolingfluid into cooling coils 18.

Drying medium 24 in liquid form collects in the bottom of vapordryer-chamber 12. Drying medium 24 is preferably isopropyl alcohol(IPA). Alternatively, drying medium 24 may comprise another processfluid suitable for the desired vapor dryer processing.

The present embodiment shows vapor drying chamber 12 operable to processa single boat 20 of substrate wafers 22. Alternatively, vapor dryerchamber 12 may be sized to process a plurality of boats 20, each holdinga plurality of substrate wafers 22.

Heater 16 heats drying medium 24, preferably producing drying mediumvapor 26. As drying medium vapor 26 rises within vapor dryer chamber 12,cooling coils 18 act to condense drying medium vapor 26. Condenseddrying medium preferably travels down the interior walls of the vapordryer chamber 12, collecting in the pool of drying medium 24 at thebottom of vapor dryer chamber 12. The interaction between heater 16vaporizing liquid drying medium 24 and cooling coils 18 condensingdrying medium vapor preferably produces a cloud of drying medium vapor26. This cloud of drying medium vapor 26 preferably has a vapor blanket28 within vapor dryer chamber 12. Vapor blanket 28 represents the upperboundary of drying medium vapor cloud 26. When vapor dryer chamber 12reaches a steady state, vapor blanket 28 is preferably above boat 20 andwafers 22.

Vapor dryer chamber 12 is preferably sized for processing boat 20holding wafers 22. Boat 20 may be loaded manually or by suitableautomated transfer equipment. Vapor dryer chamber 12 may include one ormore exhaust conduits (not expressly shown) for regulating the vapordryer chamber 12 environment.

Vapor concentration monitor assembly 30 preferably includes monitorinlet 36 in fluid communication with monitor outlet 34. Monitor 38 ispreferably in fluid communication with monitor outlet 34. Controller 40is preferably in electrical communication with monitor 38. Dilutionsupply 32 is in fluid communication with monitor inlet 36 and monitoroutlet 34.

Dilution supply 32 may be in fluid communication with a dilution system(not expressly shown) for introducing a dilution fluid, such as nitrogenor another inert gas, to dilute fluid entering monitor inlet 36.Dilution supply 32 may be operable to selectively dilute fluid flow fromvapor dryer chamber 12 to prevent saturating monitor 38.

Monitor 38 is operable to determine the vapor concentration of vaportraveling through monitor outlet 34. For one application monitor 38 maydetermine the IPA vapor concentration of the vapor traveling throughmonitor outlet 34. For one application monitor 38 may be a vaporconcentration monitor, such as IPA vapor concentration monitor modelSD-703RI-AS sold by RKI instruments. Controller 40 is in electricalcommunication with monitor 38 and preferably records vapor concentrationdata determined by monitor 38.

Vapor concentration monitor 30 is preferably positioned within vapordryer chamber 30 such that monitor inlet 36 is operable to determine thevapor concentration at a desired vapor blanket level 28. Vaporconcentration monitor 30 may by selectively positionable within vapordryer chamber 12 to allow for the selective monitoring of differentareas of vapor dryer chamber 12.

FIG. 2 is a flow diagram showing a method for controlling a vapor dryingprocess incorporating teachings of the present invention. The methodbegins with initiating the vapor dryer 50. This step involves heatingliquid drying medium 24 within vapor dryer chamber 12 while condensingdrying medium vapor until a desired steady state has been reached. Thedesired steady state is reached when a cloud of vapor having an upperboundary at the desired height within the vapor dryer is formed andmaintained. Next, controller 40 may determine whether vapor chamber 12is ready to begin processing 52 using vapor concentration data frommonitor 38. If vapor dryer chamber 12 is not properly initiated andready for processing, the initiation step 50 is repeated. If vapor dryerchamber 12 is ready for processing, the vapor dryer lid 14 is opened 54.

After lid 14 is opened 54, boat 20 and wafers 22 are placed in the dryer56. The dryer lid 14 is then closed 58. Heater 16 continues to supplyheat to the drying medium 60 and the cooling coils 18 continue tocondense the drying medium vapor. Vapor concentration monitor 30measures the concentration of the drying medium vapor within vapor dryerchamber 12. In one embodiment, vapor concentration monitor 30 measures adiluted vapor concentration to prevent the saturation of monitor 30.Controller 40 monitors the drying cycle by evaluating measurement ofvapor concentration received from monitor 38.

Controller 40 determines whether an end point to the vapor process cyclehas been reached before a predetermined cycle end point. Often,determining whether an end point has been reached includes evaluatingthe vapor concentration measured by monitor 38 to determine whether thevapor dryer chamber 12 has maintained the desired vapor concentrationfor a desired length of time 62. If an end point has been reached early,the lid 14 of the vapor dryer chamber 12 may be opened 70 and boat maybe removed 72.

If an end point is not reached early, controller 40 preferablydetermines whether an excursion within the process cycle is recorded 64.The excursion may be any significant variation in vapor concentrationmeasured by the vapor concentration monitor 30 during vapor dryerprocessing. If an excursion is recorded, the excursion is preferablynoted 66 by controller 40. The excursion may also be a determinationthat an end point was not reached during a predetermined length of time.The excursion may be noted by flagging the data representing theexcursion and saving the data. The data may be saved on a computerreadable medium. Noting the excursion may further include indicating theexcursion to operators by operating a visual or audible alarm. If anexcursion is detected, the time that wafers 22 are processed in chamber12 may be extended by a set amount of time or until the excursion eventhas passed.

If no excursion is recorded, the drying process is preferably continuedfor a desired length of time 68. After such time the lid of the vapordryer chamber may be opened 70 and boat may be removed 72 from vapordryer chamber 12.

In an alternative embodiment, controller 40 may continuously evaluatethe dryer process cycle to determine whether an end point has beenreached. In another alternative embodiment, controller 40 mayperiodically evaluate the dryer process cycle to determine whether anend point has been reached. In yet another alternative embodiment, thecontroller may be further operable to continuously or periodicallyevaluate whether an excursion has been recorded.

While the disclosed embodiments have been described in detail, it shouldbe understood that various changes, substitutions and alternations canbe made to the embodiments without departing from their spirit andscope.

What is claimed is:
 1. A method for monitoring a vapor drying processduring semiconductor fabrication comprising: providing a vapor monitorin a vapor dryer chamber; measuring vapor concentration at a selectedlevel of the vapor dryer chamber; recording the vapor concentrationmeasurement; and controlling the vapor drying process using the vaporconcentration measurement.
 2. The method of claim 1 wherein measuringvapor concentration further comprises measuring an isopropyl alcoholvapor concentration within the vapor dryer chamber.
 3. The method ofclaim 1 further comprising: initiating the vapor dryer chamber; placingat least one substrate wafer in the vapor dryer chamber; determiningwhether the vapor drying process reaches an end point; and removing theat least one substrate wafer when an end point has been reached.
 4. Themethod of claim 1 further comprising: initiating the vapor dryerchamber; determining an initial steady state point using the vaporconcentration measurement; and placing at least one substrate wafer inthe vapor dryer chamber after the initial steady state point.
 5. Themethod of claim 1 wherein controlling the process further comprises:determining whether the vapor drying process experiences a processexcursion; and flagging the vapor concentration measurement thatrepresents the process excursion.
 6. The method of claim 1 wherein theselected level comprises a vapor cloud steady state blanket level. 7.The method of claim 1 wherein controlling the process further comprises:detecting a process excursion; and extending the vapor drying processfor a set period of time.
 8. The method of claim 1 wherein controllingthe process further comprises: detecting a process excursion; andextending the vapor drying process until the process excursion haspassed.